Benzoxazine-based monomer, polymer thereof, electrode for fuel cell including the same, electrolyte membrane for fuel cell including the same, and fuel cell using the same

ABSTRACT

A benzoxazine-based monomer, a polymer thereof, an electrode for a fuel cell including the same, an electrolyte membrane for a fuel cell including the same, and a fuel cell using the same. The aromatic ring may contain up to 2 nitrogens within the ring. Single ring and fused ring substituents are attached to the pendent nitrogen. The ring substituents may be heterocyclic.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This is a divisional application of U.S. patent application Ser. No.12/208,664, filed Sep. 11, 2008, now U.S. Pat. No. 8,252,890, issuedAug. 28, 2012, which claims the benefit of Korean Patent Application No.10-2007-0092146 , filed on Sep. 11, 2007 in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein intheir entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a benzoxazine-based monomer,a polymer thereof, an electrode for a fuel cell including the same, anelectrolyte membrane for a fuel cell including the same, and a fuel cellusing the same. For purposes of this application, “benzoxazine-basedmonomer” shall mean that the aromatic ring may contain up to 2 nitrogenswithin the ring. Single ring and fused ring substituents are attached tothe pendent nitrogen. The ring substituents may be heterocyclic.

2. Description of the Related Art

Fuel cells using a polymer electrolyte membrane as an electrolyte, whichoperate at a relatively low temperature and can be miniaturized, areregarded as an alternative power source for automobiles and forresidential distributed power generation systems. A known polymerelectrolyte membrane used in polymer electrolyte membrane fuel cells arethe perfluorosulfonic acid polymers represented by NAFION® (DuPontCompany).

However, these polymer electrolyte membranes must be hydrated to retainproton conductivity. In addition, the fuel cell system needs to beoperated at 100° C. or higher in order to improve the system efficiency.However, the electrolyte membrane cannot function as a solid electrolyteat such a high temperature since moisture evaporates from theelectrolyte membrane.

A non-hydrated electrolyte membrane that can be operated at 100° C. orhigher has been developed in order to overcome these problems. Forexample, polybenzimidazole doped with phosphoric acid as a material usedto form a non-hydrated electrolyte membrane is disclosed in U.S. Pat.No. 5,525,436.

In addition, in fuel cells using a perfluorosulfonic acid polymermembrane that operates at a low-temperature, a hydrophobic electrodeobtained by mixing the perfluorosulfonic acid polymer withwater-repellent polytetrafluoroethylene (PTFE) is used in order toimprove gas diffusion that is otherwise blocked by water generated in acathode (Japanese Patent Laid-Open Publication No. hei 05-283082).

Meanwhile, in fuel cells using polybenzimidazole (PBI) doped withphosphoric acid, which is a high-temperature non-hydrated electrolytefor an electrolyte membrane, attempts to impregnate an electrode withliquid state phosphoric acid have been made and attempts to increase theloading amount of a metal catalyst have been made in order to facilitateinterface contact between the electrode and the membrane. Theseattempts, however, do not sufficiently improve characteristics of thefuel cells.

When air is supplied to a cathode in a solid polymer electrolytemembrane doped with phosphoric acid, activation takes about a week evenif the electrode composition is optimized. Although a fuel cell can haveimproved efficiency and activation time can be decreased by replacingair with oxygen, the use of oxygen is not preferred forcommercialization.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a benzoxazine-based monomerhaving improved wettability of phosphoric acid in an electrode, highthermal resistance, high phosphoric acid resistance and excellentaffinity for an acid; a polymer of the benzoxazine-based monomer; anelectrode for a fuel cell including the same; an electrolyte membranefor a fuel cell including the same; and a fuel cell using the same.

An embodiment of the present invention provides a benzoxazine-basedmonomer represented by Formula 1 below.

Here, A, B, C, D and E are carbon, or one or two of A, B, C, D and E arenitrogen and the others are carbon, and

R₁ and R₂ are connected to each other to form a ring,

wherein the ring is a C6-C10 cycloalkyl group, a C3-C10 heteroarylgroup, a fused C3-C10 heteroaryl group, a C3-C10 heterocyclic group or afused C3-C10 heterocyclic group.

Another embodiment of the present invention provides a polymer of abenzoxazine-based monomer that is a polymerization product of thebenzoxazine-based monomer or a polymerization product of thebenzoxazine-based monomer and a crosslinkable compound.

Another embodiment of the present invention provides an electrode for afuel cell including the polymer of a benzoxazine-based monomer and acatalyst. Another embodiment of the present invention provides anelectrolyte membrane for a fuel cell including a polymer of apolybenzoxazine-based compound that is a polymerization product of thebenzoxazine-based monomer and a crosslinkable compound. Anotherembodiment of the present invention provides a fuel cell including theelectrode. Another embodiment of the present invention provides a fuelcell including the electrolyte membrane.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a graph illustrating the current density-voltagecharacteristics of a fuel cell prepared according to Example 1;

FIG. 2A is a nuclear magnetic resonance (NMR) spectrum of 3HP-3AP,represented by Formula 15, prepared according to Synthesis Example 1;

FIG. 2B is an expanded portion of FIG. 2A;

FIG. 3A is a nuclear magnetic resonance (NMR) spectrum of 8HQD-3AP,represented by Formula 7, prepared according to Synthesis Example 2;

FIG. 3B is an expanded portion of FIG. 3A;

FIG. 4 is a graph illustrating the results of a thermogravimetricanalysis of 3HP-3AP, represented by Formula 15, prepared according toSynthesis Example 1 and the polymer of 3HP-3AP, represented by Formula15, and PBI prepared according to Synthesis Example 4;

FIG. 5 is a graph illustrating voltage with respect to current densityof a fuel cell prepared according to Example 4 of the present invention;

FIG. 6 is a graph illustrating cell voltage over time of a fuel cellprepared according to Example 4 of the present invention;

FIG. 7 is a graph illustrating conductivity with respect to temperatureof electrolyte membranes prepared according to Examples 4 and 5 of thepresent invention;

FIG. 8 is a graph illustrating the phosphoric acid doping level ofelectrolyte membranes prepared according to Examples 4 and 5 of thepresent invention;

FIG. 9 is a graph illustrating a solid nuclear magnetic resonance (NMR)spectrum of a solid-phase polymer of 3HP-3AP, represented by Formula 15,and PBI prepared according to Synthesis Example 4 of the presentinvention; and

FIG. 10 is a graph illustrating cell voltage with respect to currentdensity of fuel cells prepared according to Example 6 and ComparativeExample 2 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The embodiments are described below in order to explain thepresent invention by referring to the figures.

An embodiment of the present invention provides a benzoxazine-basedmonomer represented by Formula 1.

Here, A, B, C, D and E are carbon, or one or two of A, B, C, D and E arenitrogen and the others are carbon,

R₁ and R₂ are connected to each other to form a ring,

and the ring is a C6-C10 cycloalkyl group, a C3-C10 heteroaryl group, afused C3-C10 heteroaryl group, a C3-C10 heterocyclic group or a fusedC3-C10 heterocyclic group.

The ring formed by R₁ and R₂ in Formula 1 may be represented by theformulae below.

Here, R₃ to R₇ are each independently a hydrogen atom, a C1-C10 alkylgroup, a C6-C10 aryl group, a halogen atom, a cyano group, a hydroxylgroup, a C6-C10 cycloalkyl group, a C1-C10 heteroaryl group or a C1-C10heterocyclic group, wherein *a is bonded to Formula 1 at R₁ 1 and *b isbonded to Formula 1 at R₂.

The

of Formula 1 is represented by the formulae below.

The benzoxazine-based monomer according to an embodiment of the presentinvention has a structure capable of improving affinity for an acid.According to an embodiment of the present invention, when thebenzoxazine-based monomer represented by Formula 10, below, is added toan electrode for a fuel cell, the benzoxazine-based monomer of Formula10 is transformed to a structure having a plurality of quaternary aminesthrough ring opening polymerization while the fuel cell is operating andthus traps an acid as shown in Reaction Scheme 1.

Due to the acid-trapping function of the benzoxazine-based monomer, thebenzoxazine-based monomer in an electrode for a fuel cell improveswettability of phosphoric acid (H₃PO₄) to the electrode, thermalresistance and phosphoric acid resistance. In addition, since phosphoricacid is retained in micropores of the electrode, flooding caused byphosphoric acid infiltrating into macropores of the electrode, whichinhibits gas diffusion because of the large amount of liquid statephosphoric acid in the electrode, can be effectively prevented.Accordingly, comparability can be increased in the interfaces among thegaseous state (fuel gas or oxidizing gas)—the liquid state (phosphoricacid)—and the solid state (catalyst). In addition, the benzoxazine-basedmonomer is self polymerized by heat generated at an operatingtemperature to form a thermosetting polymer, which improves thestability of interfaces of the electrode.

The benzoxazine-based monomer may be one of the compounds represented byFormulae 1A to 1D.

Here, R is a hydrogen atom or a C1-C10 alkyl group.

Here, the

of Formulae 1A to 1D is represented by the formulae below.

The benzoxazine-based monomer represented by Formula 1 can besynthesized using a phenol compound having a pyridine or pyridinederivative as a starting material, an amine compound and p-formaldehyde.The conditions for the reaction are not limited. For example, thereaction can be performed by a melt process without a solvent at atemperature in the range of 80 to 100° C., and the temperature may varyaccording to the types of substituents.

Hereinafter, a method of preparing the benzoxazine-based monomerrepresented by Formula 1 according to aspects of the present inventionwill be described. For example, compounds represented by Formulae 1A and1B are described, but other compounds can be synthesized in a similarmanner.

First, as shown in Reaction Scheme 2, below, the benzoxazine-basedmonomers represented by Formulae 1A and Formula 1B can be prepared byheating a mixture of 8-hydroxyquinoline (A), p-formaldehyde (B) and anamine compound (C) without a solvent, or can be prepared by adding asolvent to the mixture, refluxing the mixture, and performing a work-upprocess of the resultant.

Here, R is a hydrogen atom or a C1-C10 alkyl group, and

-Q is

which is one of the formulae below.

When a solvent is used, 1,4-dioxane, chloroform, dichloromethane,tetrahydrofuran (THF), or the like can be used as the solvent. Theheating temperature may be in the range of 50 to 90° C. and preferablyabout 80° C., and can be adjusted to a temperature at which the solventcan be refluxed.

The benzoxazine-based monomer represented by Formula 1 according to anembodiment of the present invention may be compounds represented byFormulae 2 to 21.

A benzoxazine-based monomer according to an embodiment of the presentinvention has good affinity for acids generally, a high phosphoric acidresistance and high thermal resistance. When used in the preparation ofan electrode and an electrolyte membrane for a fuel cell, thebenzoxazine-based monomer can have a tertiary amine structure in whichthe backbone of the main chain has an affinity for phosphoric acidthrough ring-opening polymerization. In other words, the affinity forphosphoric acid is increased to maximize the capacity of phosphoricacid. Thus, wettability of phosphoric acid (H₃PO₄) at the three phaseinterface of the electrode can be improved and the amount of phosphoricacid flowing into the electrode can be increased. Particularly, oxygenpermeation can be improved, and wettability of phosphoric acid (H₃PO₄)and thermal stability can be improved in the electrode even when air isused in a cathode. Therefore, the fuel cells employing the electrode andthe electrolyte membrane including the benzoxazine-based monomer canhave excellent utility, high conductivity, and long lifetime, and canoperate at a high temperature with no humidity, and can have excellentpower generation efficiency.

Examples of the C1-C20 alkyl group are a methyl group, an ethyl group, apropyl group, an isobutyl group, a sec-butyl group, a pentyl group, aniso-amyl group, and a hexyl group, and at least one of the hydrogenatoms can be substituted with a halogen atom, a C1-C20 alkyl groupsubstituted with a halogen atom (e.g.: CCF₃, CHCF₂, CH₂F and CCl₃), ahydroxyl group, a nitro group, a cyano group, an amino group, an amidinogroup, a hydrazine, a hydrazone, a carboxyl group or a salt thereof, asulfonic acid group or a salt thereof, a phosphoric acid or a saltthereof, a saturated C1-C20 alkyl group, a C2-C20 alkenyl group, aC2-C20 alkynyl group, a C1-C20 heteroalkyl group, a C6-C20 aryl group, aC6-C20 arylalkyl group, a C6-C20 heteroaryl group or a C6-C20heteroarylalkyl group.

The aryl group as used herein is used alone or in a combination, and isa carbocyclic aromatic system having 6 to 20 carbon atoms and one ormore rings. The rings can be attached to each other or fused with eachother using a pendent method. The term “aryl” includes an aromaticradical such as phenyl, naphthyl, and tetrahydronapththyl. The arylgroup may include a substituent of a haloalkylene group, a nitro group,a cyano group, an alkoxy group, and a short chain alkylamino group. Inaddition, at least one of the hydrogen atoms can be substituted with thesame functional groups described above for the C1-C20 alkyl group.

The heteroaryl group as used herein indicates a monovalent monocyclic orbivalent bicyclic aromatic organic compound including C1-C20 carbonrings and including 1, 2, or 3 hetero atoms selected from the groupconsisting of nitrogen, oxygen, phosphorus and sulfur. Examples of theheteroaryl group are pyrazinyl, furanyl, thienyl, pyridyl, pyrimidinyl,isothiazolyl, oxazolyl, thiazolyl, triazolyl and 1,2,4-thiadiazolyl.

The fused heteroaryl group as used herein indicates a single-ring ordouble-ring system composed of about 8 to 11 rings in which at least oneatom is an atom other than a carbon atom, such as nitrogen, oxygen orsulfur.

At least one of the hydrogen atoms of the heteroaryl group and the fusedheteroaryl group can be substituted with the same functional groupsdescribed above for the C1-C20 alkyl group.

The heterocyclic group as used herein indicates five-ten-membered ringincluding hetero atoms such as nitrogen, sulfur, phosphor and oxygen. Atleast one of the hydrogen atoms of the heterocyclic group can besubstituted with the same functional groups described above for theC1-C20 alkyl group. The fused heterocyclic group as used herein is asingle-ring or double-ring system of the heterocyclic group.

The C6-C10 cycloalkyl group as used herein indicates a carbocycle having6 to 10 carbon atoms, and at least one of hydrogen atoms can besubstituted with the same functional groups described above for theC1-C20 alkyl group.

Aspects of the present invention also provide a polymer of thebenzoxazine-based monomer that is a polymerization product of thebenzoxazine-based monomer represented by Formula 1. The polymer can beprepared by dissolving the benzoxazine-based monomer in a solvent andpolymerizing the solution through heat-treatment. The heat-treatment maybe performed at a temperature in the range of 150 to 240° C. When theheat-treatment temperature is less than 150° C., the extent of thepolymerization reaction may be decreased. On the other hand, when thetemperature is higher than 240° C., other compounds or polymersgenerated from side reactions may decrease yields of the desiredproducts. A polymerization catalyst can be used, if required. Thesolvent may be N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), orthe like, and the amount of the solvent may be in the range of 5 to 95parts by weight based on 100 parts by weight of benzoxazine-basedmonomer.

An embodiment of the present invention also provides a polymer of abenzoxazine-based monomer that is a polymerization product of thebenzoxazine-based monomer represented by Formula 1 and a crosslinkablecompound. The crosslinkable compound may be at least one ofpolybenzimidazole (P81), a polybenzimidazole-base complex,polybenzthiazole, polybenzoxazole and polyimide, but is not limitedthereto. The amount of the crosslinkable compound may be in the range of5 to 95 parts by weight based on 100 parts by weight of thebenzoxazine-based monomer represented by Formula 1.

An electrode for a fuel cell according to an embodiment of the presentinvention includes a catalyst layer incorporating a polymer that is apolymerization product of the benzoxazine-based monomer represented byFormula 1 or a polymerization product of the benzoxazine-based monomerrepresented by Formula 1 and the crosslinkable compound. The catalystlayer includes a catalyst.

The polymer of the benzoxazine-based monomer represented by Formula 1 isalso used as a binder for the electrode, and thus a conventional binderis not necessary. The polymer of the benzoxazine-based monomerrepresented by Formula 1 improves the wettability of phosphoric acid.The amount of the polymer may be in the range of 0.1 to 65 parts byweight based on 100 parts by weight of the catalyst. When the amount ofthe polymer is less than 0.1 parts by weight, the wet state of theelectrode is not sufficiently improved. On the other hand, when theamount of the polymer is greater than 65 parts by weight, flooding maybe increased.

The catalyst may be Pt, a metal-Pt alloy including Pt and at least onemetal selected from the group consisting of Au, Pd, Rh, Ir, Ru, Sn, Mo,Co, and Cr, or a mixture including Pt and at least one metal selectedfrom the group consisting of Au, Pd, Rh, Ir, Ru, Sn, Mo, Co, and Cr.Alternatively, the catalyst may be a support catalyst in which thecatalyst metal is loaded on a carbonaceous support. In particular, thecatalyst may be a catalyst metal including at least one of Pt, PtCo, andPtRu, or a support catalyst in which the catalyst metal is loaded on acarbonaceous support.

The electrode according to an embodiment of the present invention mayfurther include a binder that is commonly used in the preparation of anelectrode for fuel cells. The binder may be at least one ofpoly(vinylidenefluoride), polytetrafluoroethylene, atetrafluoroethylene-hexafluoroethylene copolymer, and perfluoroethylene,and for improving wettability of the electrode the amount of the bindermay be in the range of 0.1 to 50 parts by weight based on 100 parts byweight of the catalyst.

The crosslinkable compound may be at least one of polybenzimidazole(PBI), a polybenzimidazole-base complex, polybenzthiazole;polybenzoxazole and polyimide, but is not limited thereto. The amount ofthe crosslinkable compound may be in the range of 5 to 95 parts byweight based on 100 parts by weight of the benzoxazine-based monomerrepresented by Formula 1.

A method of preparing the electrode for a fuel cell will be described.First, a catalyst is dispersed in a solvent to prepare a dispersion. Thesolvent may be N-methylpyrrolidone (NMP), DMAc, or the like, and theamount of the solvent may be in the range of 100 to 1000 parts by weightbased on 100 parts by weight of the catalyst. A mixture of abenzoxazine-based monomer represented by Formula 1, a solvent and abinder is added to the dispersion and mixed while stirring. The mixturemay further include a crosslinkable compound. The solvent may beN-methylpyrrolidone (NMP), dimethyl acetamide (DMAc), or the like.

An electrode is prepared by coating the mixture on the surface of acarbon support. Here, the carbon support may be fixed on a glasssubstrate in order to facilitate coating. The coating can be performedusing a doctor blade, a bar coating, screen printing, or the like, butthe coating method is not limited thereto.

The coated mixture is dried at a temperature in the range of 20 to 150°C. to remove the solvent. The drying may be performed for 10 to 60minutes, and the drying time may vary according to the dryingtemperature.

As described above, the electrode for a fuel cell does not include thebenzoxazine-based monomer represented by Formula 1 but a polymer thereofsince the benzoxazine-based monomer represented by Formula 1 ispolymerized to form the polymer while the electrode is activated and/orwhile the fuel cell is operated. If a crosslinking agent is furtheradded to the mixture of the benzoxazine-based monomer, the solvent, andthe binder, the prepared electrode includes a polymer of thebenzoxazine-based monomer and the crosslinkable compound.

Hereinafter, an electrolyte membrane and a method of preparing theelectrolyte membrane according to an embodiment of the present inventionwill be described. An electrolyte membrane formed using a crosslinkablecompound is described herein. However, when an electrolyte membrane isprepared only using the benzoxazine-based monomer represented by Formula1, the preparation process is the same as that described herein, exceptthat the crosslinkable compound is not used.

First, a phosphorus-containing benzoxazine-based monomer represented byFormula 1 is blended with a crosslinkable compound, and the mixture iscured at a temperature in the range of 50 to 250° C., and preferably 80to 220° C. The cured mixture is impregnated with a proton conductor suchas an acid to prepare an electrolyte membrane.

The crosslinkable compound may be at least one compound selected fromthe group consisting of polybenzimidazole (PBI), apolybenzimidazole-base complex, polybenzthiazole, polybenzoxazole, andpolyimide. The polybenzimidazole-base complex is disclosed in KoreanPatent Application No. 2007-102579 filed by the inventors of the presentinvention.

The amount of the crosslinkable compound may be in the range of 5 to 95parts by weight based on 100 parts by weight of the benzoxazine-basedmonomer of Formula 1.

When the amount of the crosslinkable compound is less than 5 parts byweight, the proton conductivity may be decreased since phosphoric acidcannot be impregnated into the membrane. On the other hand, when theamount of the crosslinkable compound is greater than 95 parts by weight,gas may permeate since the crosslinked polybenzoxazines melt inpolyphosphoric acid in the presence of an excessive amount of phosphoricacid.

Second, an electrolyte membrane is formed using a mixture of the firstbenzoxazine-based monomer represented by Formula 1 and the crosslinkablecompound. The membrane may be formed using tape casting, or aconventionally used coating method. The coating method may be a methodof casting the mixture on a support using a doctor blade. In thisregard, the doctor blade having a 250-500 μm gap may be used.

In the formation of the membrane using the doctor blade method, aprocess of removing the support by exfoliating the electrolyte membranefrom the support may further be included after the curing and before theimpregnation with the proton conductor. In order to remove the support,the membrane may be immersed in distilled water at a temperature in therange of 60 to 80° C.

The support may be any material that can support the electrolytemembrane, for example, a glass substrate, polyimide film, and the like.Removal of the support by immersion is not necessary in the tape castingmethod, since the tape cast membrane is stripped from a support such aspolyethylene terephthalate and placed in an oven for curing. Inaddition, when the membrane is formed using a mixture ofbenzoxazine-based monomer and polybenzimidazole through a tape castingmethod, filtering the mixture may further be included in the method.

The prepared membrane is cured through heat treatment, and impregnatedwith a proton conductor such as an acid to form an electrolyte membrane.The proton conductor may be phosphoric acid, a C1-C20 organic phosphonicacid, or the like, but is not limited thereto. The C1-C20 organicphosphonic acid may be methyl phosphonic acid, ethyl phosphonic acid,etc. The amount of the proton conductor may be 300 to 1000 parts byweight based on 100 parts by weight of the electrolyte membrane. Forexample, 85% by weight of an aqueous phosphoric acid solution may beused at 80° C. for 2.5 to 14 hours, but the concentration of the acidused in this embodiment of the present invention is not limited.

A method of preparing a fuel cell using the electrode according to anembodiment of the present invention will be described. Any electrolytemembrane that is commonly used in the preparation of fuel cells can beused herein. Alternatively, an electrolyte membrane including acrosslinked product of polybenzoxazine-based compounds that is preparedby polymerization of the benzoxazine-based monomer represented byFormula 1 and a crosslinkable compound can be used as well.

Performance of the fuel cell may be maximized by using an electrolytemembrane including the crosslinked product of polybenzoxazine-basedcompounds. For example, the electrolyte membrane may be apolybenzimidazole electrolyte membrane, apolybenzoxazine-polybenzimidazole copolymer electrolyte membrane, a PTFEporous membrane, or the like.

A process of preparing a membrane and electrode assembly for fuel cellsaccording to an embodiment of the present invention will be described.Here, the “membrane and electrode assembly (MEA)” refers to a structurein which electrodes composed of a catalyst layer and a diffusion layerare laminated on both sides of an electrolyte membrane.

The MEA according to this embodiment the present invention may beprepared by placing electrodes including the catalyst layer on bothsides of the obtained electrolyte membrane and combining them at a hightemperature under a high pressure, and then further combining them witha fuel diffusion layer. The combining may be performed at a temperatureat which the electrolyte membrane softens, that is, under 0.1 to 3ton/cm², and preferably under about 1 ton/cm².

Then, a bipolar plate is installed into each membrane-electrode assemblyto complete a fuel cell. The bipolar plate has a fuel supply groove andcurrent collecting property. The fuel cell may be used as a polymerelectrolyte membrane fuel cell (PEMFC), but is not limited thereto.

Hereinafter, aspects of the present invention will be described ingreater detail with reference to the following examples. The followingexamples are for illustrative purposes only and are not intended tolimit the scope of the invention.

Synthesis Example 1 Preparation of 3HP-3AP, represented by Formula 15

5 g (0.053 mol) of 3-hydroxypyridine, 3.67 g (0.116 mol) ofp-formaldehyde and 5.46 g (0.058 mol) of 3-aminopyridine were added to a100 ml one-neck round-bottom flask and mixed while held in an oil bathat 90° C. After about 30 minutes, when the initially opaque mixturebecame a yellow transparent gel type material, the reaction was quenchedusing chloroform, and then the mixture was cooled to room temperature.The cooled crude product was base-washed twice through solventextraction using a 1N NaOH aqueous solution, and washed once withdeionized water.

After washing, the organic layer was dried with MgSO₄ and filtered. Theresidual solution was dried using a rotary evaporator to remove thesolvent, and the purified product was dried in a vacuum oven at 40° C.for 6 hours to obtain 3HP-3AP as represented by Formula 15. Thestructure of 3HP-3AP was identified by the nuclear magnetic resonance(NMR) spectra of FIGS. 2A and 2B.

Synthesis Example 2 Preparation of 8HQD-3AP, represented by Formula 7

10 g (0.063 mol) of 8-hydroxyquinaldine, having the structure below,4.36 g (0.138 mol) of p-formaldehyde and 6.49 g (0.069 mol) of3-aminopyridine were added to a 100 ml one-neck round-bottom flask andmixed while held in an oil bath at 90° C.

After about 30 minutes, when the initially opaque mixture became ayellow transparent gel type material, the reaction was quenched usingchloroform, and then the mixture was cooled to room temperature. Thecooled crude product was base-washed twice through solvent extractionusing a 1N NaOH aqueous solution, and washed once with deionized water.

After washing, the organic layer was dried with MgSO₄ and filtered. Theresidual solution was dried using a rotary evaporator to remove thesolvent, and the purified product was dried in a vacuum oven at 40° C.for 6 hours to obtain 8HQD-3AP, represented by Formula 7. The structureof 8HQD-3AP was identified by the nuclear magnetic resonance (NMR)spectra of FIGS. 3A and 3B.

Synthesis Example 3 Preparation of 8HP-2AP, represented by Formula 14

10 g (0.069 mol) of 8-hydroxyquinoline, 4.81 g (0.152 mol)p-formaldehyde and 7.23 g (0.076 mol) of 2-aminopyridine were added to a100 ml one-neck round-bottom flask and mixed while held in an oil bathat 90° C.

After about 30 minutes, when the initially opaque mixture became ayellow transparent gel type material, the reaction was quenched usingchloroform, and then the mixture was cooled to room temperature. Thecooled crude product was base-washed twice through solvent extractionusing a 1N NaOH aqueous solution, and washed once with deionized water.

After washing, the organic layer was dried with MgSO₄ and filtered. Theresidual solution was dried using a rotary evaporator to remove thesolvent, and the purified product was dried in a vacuum oven at 40° C.for 6 hours to obtain 8HP-2AP, represented by Formula 14. As a result ofidentifying the structure of the compound by an NMR spectrum, peaksillustrating characteristics of a benzoxazine ring were observed atchemical shifts of 5.6 ppm and 4.8 ppm as shown in FIGS. 2A, 2B, 3A and3B.

Synthesis Example 4 Preparation of a polymer of 3HP-3AP, represented byFormula 15, and PBI

65 parts by weight of 3HP-3AP, represented by Formula 15 and prepared inSynthesis Example 1, was blended with 35 parts by weight ofpolybenzimidazole, and the mixture was cured at a temperature in therange of about 180 to 240° C. to obtain a polymer of 3HP-3AP,represented by Formula 15, and PBI.

The thermal stability of 3HP-3AP, represented by Formula 15 prepared inSynthesis Example 1, and the polymer of 3HP-3AP, represented by Formula15 and PBI prepared in Synthesis Example 4, were measured usingthermogravimetric analysis, and the results are shown in FIG. 4. Thethermal weight loss was measured at 800° C. in FIG. 4. Referring to FIG.4, the polymer of 3HP-3AP and PBI had higher thermal stability comparedto the 3HP-3AP monomer.

The structure of the solid-phase polymer of 3HP-3AP, represented byFormula 15 and PBI prepared in Synthesis Example 4, was identified by asolid nuclear magnetic resonance (NMR) spectrum, and the results areshown in FIG. 9. The NMR was performed using a Varian Unity INOVA600 at600 MHz.

Example 1 Preparation of an Electrode for a Fuel Cell and a Fuel CellUsing the Electrode

1 g of a catalyst, in which 50% by weight of PtCo is supported oncarbon, and 3 g of NMP as a solvent were added to a container, and themixture was agitated using a mortar to prepare a slurry. A solution of3% by weight of 3HP-3AP, represented by Formula 15 prepared according toSynthesis Example 1, and NMP was added to the slurry and stirred toprepare 0.025 g of the compound represented by Formula 15.

Then, a solution of 5% by weight of polyvinylidenefluoride and NMP wasadded to the mixture to set the amount of the polyvinylidenefluoride to0.025 g, and the mixture was stirred for 10 minutes to prepare a slurryfor a cathode catalyst layer. Carbon paper was cut into pieces of 47 cm²in size, and the pieces were fixed on a glass plate and coated using adoctor blade (Sheen instrument), wherein the gap interval of the doctorblade was 600 μm. The slurry for a cathode catalyst layer was coated onthe carbon paper and dried at room temperature for 1 hour, at 80° C. for1 hour, at 120° C. for 30 minutes and at 150° C. for 15 minutes toprepare a cathode (a fuel electrode). The amount of loaded Pt/Co in theprepared cathode was 3.0 mg/cm².

An electrode prepared according to the following process was used as ananode. 2 g of a catalyst in which 50% by weight of Pt is supported oncarbon and 9 g of NMP solvent were added to a container and the mixturewas agitated in a high-speed agitator for 2 minutes.

Then, a solution of 0.05 g of polyvinylidenefluoride dissolved in 1 g ofNMP was added thereto and agitated for 2 minutes to prepare a slurry foran anode catalyst layer. The slurry was coated on carbon paper on whicha microporous layer had been coated, using a bar coater. The amount ofloaded Pt in the prepared anode was 1.4 mg/cm².

65 parts by weight of benzoxazine-based monomer, represented by theformula below, and 35 parts by weight of polybenzimidazole were blended,and cured at a temperature in the range of 180 to 240° C.

Then, to prepare an electrolyte membrane, the resultant was impregnatedwith 85% by weight of phosphoric acid at 80° C. for longer than 4 hours.Here, the amount of phosphoric acid was about 450 parts by weight basedon 100 parts by weight of electrolyte membrane. The amount of loadedPt/Co in the prepared cathode was about 2.17 mg/cm², and the amount ofloaded Pt in the prepared anode was 1.5 mg/cm².

A membrane electrode assembly (MEA) was prepared by interposing theelectrolyte membrane between the cathode and the anode. Here, thecathode and anode were not impregnated with phosphoric acid.

A 200 μm PTFE membrane for a main gasket and a 20 μm PTFE membrane for asub gasket were overlapped on an interface between the electrodes andelectrolyte membrane in order to prevent gas permeation between thecathode and the anode. In order to assemble a cell, the pressure appliedto the MEA was adjusted to 1, 2, 3 N-m Torque, step by step, using awrench.

Characteristics of fuel cells were measured while operating by supplyinghydrogen to the anode at 100 ccm and supplying air to the cathode at 250ccm at 150° C. while the electrolyte membrane was not hydrated. Sincecell efficiency increases with time by using the electrolyte doped withphosphoric acid, the final efficiency was measured after the fuel cellwas activated and was performed until the operational voltage wasmaximized. The area of the cathode and the anode was fixed to 2.82.8=7.84 cm², and the thickness of the cathode was about 430 μm and thethickness of the anode was about 390 μm, although the thicknesses of thecathode and the anode may vary according to the distribution ofthickness of the carbon paper.

Example 2 Preparation of an Electrode for a Fuel Cell and a Fuel CellUsing the Electrode

A cathode and a fuel cell using the cathode were prepared in the samemanner as in Example 1, except that 8HP-2AP, represented by Formula 14prepared according to Synthesis Example 2, was used instead of 3HP-3AP,represented by Formula 15, in the preparation of the cathode.

Example 3 Preparation of an Electrode for a Fuel Cell and a Fuel CellUsing the Electrode

A cathode and a fuel cell using the cathode were prepared in the samemanner as in Example 1, except that 8HQD-3AP, represented by Formula 7prepared according to Synthesis Example 3, was used instead of 3HP-3AP,represented by Formula 15, in the preparation of the cathode.

Comparative Example 1 Preparation of an Electrode for a Fuel Cell and aFuel Cell Using the Electrode

A cathode and a fuel cell using the cathode were prepared in the samemanner as in Example 1, except that 3HP-3AP, represented by Formula 15,was not added in the preparation of the cathode.

In addition, cell potential changes as a function of current densitywere measured in fuel cells prepared according to Example 1 andComparative Example 1, and the results are shown in FIG. 1. The d1, d3,d5 and d7 of FIG. 1 respectively indicate first day, third day, fifthday and seventh day. Referring to FIG. 1, high potentials of fuel cellscan be maintained with the passage of time.

The performance of fuel cells prepared according to Examples 1 to 3 andComparative Example 1 was tested and the results are shown in Table 1.

TABLE 1 Time taken to reach 95% of the Voltage at Tafel's slope maximumvoltage 0.3 A/cm² (V) (mV/sec) (hr) Compound of 0.667 75 60 Formula 14(Example 2) Compound of 0.657 79 80 Formula 7 (Example 3) Compound of0.671 95 100 Formula 15 (Example 1) Comparative 0.678-0.692 97-100 100Example 1

According to Table 1, the voltage characteristics of fuel cells ofExamples 1 to 3, which include an additive having high affinity forphosphoric acid, were improved compared to that of Comparative Example1, since reduction in the reactivity of the oxygen/reduction reaction(ORR) due to phosphoric acid was inhibited.

As shown in Table 1, the Tafel's slopes of Examples 1 to 3 are lowerthan that of Comparative Example 1, and thus it can be seen that the ORRmechanism was changed. In addition, the fuel cells of Examples 1 to 3can reach the maximum voltage more quickly than the fuel cell ofComparative Example 1 since t fuel cells of Examples 1 to 3 haveexcellent affinity to phosphoric acid.

Example 4 Preparation of an Electrolyte Membrane for a Fuel Cell and aFuel Cell Using the Electrolyte Membrane

1 g of a catalyst in which 50% by weight of PtCo is loaded on carbon and3 g of NMP as a solvent were added to a container, and the mixture wasagitated using a mortar to prepare a slurry. Then, a solution of 5% byweight of polyvinylidenefluoride and NMP was added to the mixture to setthe amount of the polyvinylidenefluoride to 0.025 g, and the mixture wasstirred for 10 minutes to prepare a slurry for a cathode catalyst layer.

Carbon paper was cut into pieces of 47 cm² in size, and the pieces werefixed on a glass plate and coated using a doctor blade (Sheeninstrument), wherein the gap interval of the doctor blade was 600 Theslurry for a cathode catalyst layer was coated on the carbon paper anddried at room temperature for 1 hour, at 80° C. for 1 hour, at 120° C.for 30 minutes and at 150° C. for 15 minutes to prepare a cathode (afuel electrode). The amount of loaded Pt/Co in the prepared cathode was3.0 mg/cm².

An electrode prepared according to the following process was used as ananode. 2 g of a catalyst in which 50% by weight of Pt is supported oncarbon and 9 g of NMP solvent were added to a container and the mixturewas agitated in a high-speed agitator for 2 minutes. Then, a solution of0.05 g of polyvinylidenefluoride dissolved in 1 g of NMP was addedthereto and agitated for 2 minutes to prepare a slurry for an anodecatalyst layer. The slurry was coated on carbon paper on which amicroporous layer had been coated, using a bar coater. The amount ofloaded Pt in the prepared anode was 1.4 mg/cm².

65 parts by weight of 3HP-3AP represented by Formula 15 prepared inSynthesis Example 1 was blended with 35 parts by weight of PBI, and themixture was cured at about 220° C.

Then, the resultant was impregnated with 85% by weight of phosphoricacid at 80° C. for longer than 4 hours to prepare an electrolytemembrane. Here, the amount of phosphoric acid was about 530 parts byweight based on 100 parts by weight of electrolyte membrane.

A membrane electrode assembly (MEA) was prepared by interposing theelectrolyte membrane between the cathode and the anode. Here, thecathode and anode were not impregnated with phosphoric acid.

A 200 μm PTFE membrane for a main gasket and a 20 μm PTFE membrane for asub gasket were overlapped on an interface between the electrodes andelectrolyte membrane in order to prevent gas permeation, between thecathode and the anode. In order to assemble a cell, pressure applied tothe MEA was adjusted, step by step, to 1, 2, 3 N-m Torque using awrench.

Characteristics of fuel cells were measured while operating by supplyinghydrogen to the anode at 100 ccm and supplying air to the cathode at 250ccm at 150° C. while the electrolyte membrane was not hydrated. Sincecell efficiency increases with time by using the electrolyte doped withphosphoric acid, the final efficiency was measured after the fuel cellhad aged until the operational voltage reached a maximum. The area ofthe cathode and the anode is fixed to 2.8 2.8=7.84 cm², and thethickness of the cathode was about 430 μm and the thickness of the anodewas about 390 μm, although the thicknesses of the cathode and the anodemay vary according to the distribution of thicknesses of the carbonpaper.

The voltage as a function of current density of the fuel cell preparedaccording to Example 4 was measured, and the results are shown in FIG.5. Referring to FIG. 5, the fuel cell of Example 4 had an open circuitvoltage (OCV) of 1.05 V as well as a voltage of 0.684 V at 0.3 A/cm².

Furthermore, the cell voltage over time of the fuel cell of Example 4was measured, and the results are shown in FIG. 6. In FIG. 6, “♦ OCV”denotes an open circuit voltage (OCV), and “▴ 0.2 A/cm²” denotes cellvoltage at a current density of 0.2 A/cm². Referring to FIG. 6, it canbe seen that the fuel cell of Example 4 has excellent cell voltagecharacteristics.

Example 5 Preparation of an Electrolyte Membrane for a Fuel Cell and aFuel Cell Using the Electrolyte Membrane

An electrolyte membrane and a fuel cell using the electrolyte membranewere prepared in the same manner as in Example 4, except that 8HQD-3AP,represented by Formula 7, was used instead of 3HP-3AP, represented byFormula 15, in the formation of the electrolyte membrane.

The conductivity as functions of temperature and phosphoric acid dopinglevel of the electrolyte membrane prepared in Examples 4 and 5 weremeasured, and the results are shown in FIGS. 7 and 8. Referring to FIGS.7 and 8, the electrolyte membrane of Examples 4 and 5 has higherconductivity when compared with the PBI electrolyte membrane. In FIG. 8,the doping level is shown in percentages based on the weight of theimpregnated amount of phosphoric acid.

Example 6 Preparation of a Fuel Cell

A fuel cell was prepared in the same manner as in Example 4, except that3HP-3AP, represented by Formula 15, was used in the preparation of thecathode.

Comparative Example 2 Preparation of a Fuel Cell

A fuel cell was prepared in the same manner as in Example 6, except thatPBI electrolyte membrane was used instead of 3HP-3AP, represented byFormula 15, in the preparation of the cathode and 3HP-3AP, representedby Formula 15, was not added in the preparation of the cathode.

Cell voltage characteristics with respect to the current density of fuelcells prepared in Example 6 and Comparative Example 2 were measured, andthe results are shown in FIG. 10. Referring to FIG. 10, the performanceof the MEA prepared in Example 6 was improved compared with that of theMEA prepared in Comparative Example 2.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. An electrode for a fuel cell comprising a monomer selected from the group consisting of Formulae 2 through 21 or a polymer of the monomer:


2. The electrode of claim 1, wherein the polymer is a polymerization product of the monomer or a polymerization product of the monomer and a crosslinkable compound.
 3. The electrode of claim 2, further comprising a catalyst layer comprising a catalyst.
 4. The electrode of claim 3, wherein the amount of the polymer of the monomer is in the range of 0.1 to 65 parts by weight based on 100 parts by weight of the catalyst.
 5. The electrode of claim 3, wherein the catalyst is Pt, a metal-Pt alloy including Pt and at least one metal selected from the group consisting of Au, Pd, Rh, Ir, Ru, Sn, Mo, Co, and Cr, or a mixture including Pt and at least one metal selected from the group consisting of Au, Pd, Rh, Ir, Ru, Sn, Mo, Co, and Cr.
 6. The electrode of claim 3, wherein the catalyst is a catalyst metal or a support catalyst in which the catalyst metal is loaded on a carbonaceous support, and the catalyst metal is Pt, a metal-Pt alloy including Pt and at least one metal selected from the group consisting of Au, Pd, Rh, Ir, Ru, Sn, Mo, Co, and Cr, or a mixture including Pt and at least one metal selected from the group consisting of Pt, Au, Pd, Rh, Ir, Ru, Sn, Mo, Co, and Cr.
 7. The electrode of claim 3, wherein the catalyst layer further comprises at least one proton conductor selected from the group consisting of phosphoric acid and a C1-C20 organic phosphonic acid.
 8. The electrode of claim 3, wherein the catalyst layer further comprises a catalyst and a binder, the binder is at least one polymer selected from the group consisting of poly(vinylidene fluoride), polytetrafluoroethylene (PTFE), a tetrafluoroethylene-hexafuoroethylene copolymer, fluorinated ethylene propylene (FEP), styrene butadiene rubber (SBR) and polyurethane, and the concentration of the binder is in the range of 0.1 to 50 parts by weight based on 100 parts by weight of the catalyst.
 9. The electrode of claim 2 further comprising at least one binder selected from the group consisting of poly(vinylidene fluoride), polytetrafluoroethylene (PTFE), a tetrafluoroethylene-hexafuoroethylene copolymer, fluorinated ethylene propylene (FEP), styrene butadiene rubber (SBR) and polyurethane.
 10. An electrolyte membrane for a fuel cell comprising a polymer comprising a monomer selected from the group consisting of Formulae 2 through 21:


11. The electrolyte membrane of claim 10, further comprising at least one proton conductor selected from the group consisting of phosphoric acid and a C1-C20 organic phosphonic acid.
 12. A fuel cell comprising: a cathode; an anode; and an electrolyte membrane interposed between the cathode and the anode, wherein at least one of the cathode and the anode comprises the electrode according to claim 1 which comprises a monomer selected from the group consisting of Formulae 2 through 21 or a polymer of the monomer.
 13. The fuel cell of claim 12, wherein the electrolyte membrane comprises a polymer of the monomer or a polymerization product of the monomer and a crosslinkable compound. 